<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>
        .hide {
            display: none;
        }
    </style>

    <script src="jquery-3.3.1.min.js"></script>
</head>
<body>
<div>
    <input type="button" value="" id="sub1">
</div>

<div class="hide" id="Submitbut">
    <form id="form1">
        name: <input type="text" name="username" value="">
        pwd: <input type="password" name="pwd" value="">
        phone: <input type="text" name="phone" value="">
        <input type="button" value="Submit">
    </form>
</div>


<script>
    $(function () {
        initButton()
    })

    function initButton() {
        $("#sub1").click(
            function () {
                console.log(123)
                $("#Submitbut").removeClass("hide")
            }
        )
    }
</script>

</body>
</html>